The present invention relates to a method and an apparatus for mixing loose material. More particularly, the present invention concerns mixing pulverulent or granular material.
It is known in the art, in order to mix the material in a container, to circulate by means of gas the material from the bottom of the container to the upper part thereof through a riser pipe.
It is known from experience that relatively good mixing results can be obtained using such devices only if the material to be mixed is circulated in the container from 10 to 20 times. Clearly, the result of using such devices is that too long a time is necessary to mix the material.
Another type of a mixing apparatus is known (see German Pat. Nos. 1,937,374 and 2,219,397) where in order to improve the longitudinal mixing the material fed into the riser pipe is withdrawn from two different portions of the material-columns at two different elevations and is fed in to the riser pipe through two ring channels of different respective elevation. The mixing time in such an apparatus is considerably reduced compared with the first mentioned technique, that is such an apparatus requires only two to five circulations of the material within the container. The shortest possible mixing time in such an arrangement depends upon the flowability of the material. Thus, the width of the ring channel(s) must be selected empirically in accordance with the particular material to be mixed. In the known arrangements changes of the ring-channel cross-section are possible only by axial displacement of the riser pipe. Such displacements presuppose structural complexity and expense. This is especially true when relatively large quantities of material are to be mixed. In relatively large containers having a volumetric capacity of 500 m.sup.3, the diameter of the riser pipe is up to about 1000 mm and the length up to about 30 m. Clearly such a pipe is rather difficult to precisely displace.